Method and system for operating and/or monitoring a multi-axis machine

ABSTRACT

A method for determining a response time of a brake of at least one assigned axis of a multi-axis machine includes actuating the axis, switching the brake, and determining a response time between a switching point in time and a response point in time at which a motion state of the axis changes. The method may further include opposing actuation of the axis while the brake is closed, and detecting a mechanical play between opposing maximum deflections of the axis. A method of operating or monitoring a multi-axis machine includes determining a response time and/or detecting mechanical play, and operating the machine or triggering a fault response based on the response time or mechanical play.

CROSS-REFERENCE

This application is a divisional of U.S. patent application Ser. No.15/009,957 filed Jan. 29, 2016 (pending), which claims the benefit ofGerman Patent Application No. 10 2015 001 203.7 filed Jan. 30, 2015(expired), the disclosures of which are expressly incorporated byreference herein in their entirety.

TECHNICAL FIELD

The present invention relates to a method for determining a responsetime and/or the mechanical play of a brake of an axis on a multi-axismachine, in particular on a robot, a method to operate and/or monitorthe machine by taking into account this response time and/or themechanical play, and a system and computer programming product toexecute a method described herein.

BACKGROUND

Brakes on axes of multi-axis machines, in particular such as robots,have a response time and/or closing time between a switching of thebrake and a response point in time at which the brake changes a motionstate of the assigned axis and/or effects a change of the motion state.A motion state can in particular comprise a rotational speed, a changein rotational speed, a velocity or an acceleration, and/or adeceleration of the axis. A change in velocity and/or a change inrotational speed as defined by a change and/or switch of the motionstate can for instance be defined by a relative change of the referenceparameter rotational speed and/or velocity by more than approximately 2percent, by more than approximately 5 percent, especially preferred bymore than approximately 10 percent, and in particular by more thanapproximately 20 percent. In order to effect a specified accelerationand/or deceleration, the brake needs to apply a certain minimum brakeforce to thereby change the motion state. In particular, the brake canalso brake with a (maximum) nominal brake force. Analogously, the brakeshave an opening time between a switching of the brake and a responsepoint in time, from which point forward the brake applies, or can apply,no more than only a certain maximum brake force, and in particular isfully vented and/or at least essentially applies, and/or can apply, nofurther brake force.

For purposes of a more compact description, such a closing and/oropening time is generally referred to herein as the response time of thebrake. The response time of the brake can in particular depend onmechanical, hydraulic, pneumatic, (electro-) magnetic and/or signalingtechnology and/or energy-technical inertia, brake wear, and the like.

Closed brakes also exhibit a mechanical play, by which the axis can bemoved by a certain force, in particular in the amount of the (maximum)nominal brake force. In particular, such a mechanical play can alsodepend on brake wear.

Having knowledge of a real-time response time and/or such a mechanicalplay can advantageously improve the operation and/or monitoring of themachine. For instance, if the real-time response time is known, thebrake can be switched appropriately earlier or later, instead of havingto do so on the basis of theoretical maximum and/or worst-case valuesfor track planning purposes. In the same manner, a known real-timemechanical play can for instance be taken into account for trackplanning purposes by appropriately readjusting the axis.

If a known real-time response time and/or a known real-time mechanicalplay exceeds a specified limit value, a fault state can be identified onthe machine monitored in this manner.

The task of the present invention is therefore to improve the operationand/or monitoring of a multi-axis machine, in particular a robot.

SUMMARY

According to first aspect of the present invention, a method todetermine a response time of a brake on an axis of a multi-axis machine,in particular a robot, comprises the steps:

a) actuating the axis;

b) switching the brake; and

c) determining a response time between a switching point in time of thebrake and a response point in time at which the motion state of the axischanges.

In one implementation, this involves switching the brake and determiningthe response point in time while the axis is in the process of beingactuated and/or is in the actuated state. The actuation of the brake ispreferably stopped thereafter with a predetermined time offset or todetect the response point in time. In particular, the axis can beactuated by the drive with a constant velocity until it was detectedthat the brake has engaged and/or that the response point in time hasbeen reached. This detection can for instance be accomplished withforce-moment sensors, which measure the forces and/or moments appliedbetween the drive and the axis. Alternatively, or additionally, thedetection can also be accomplished on the basis of the current draw bythe drive. In one implementation, the response time can in particular bea closing time of the brake. In one implementation, the brake is thenswitched in step b) from an opened to a closed state. The response pointin time can for instance be a point in time at which a predeterminedrotational speed change can be detected. In particular, the responsepoint in time can be defined as the time at which the rotational speedof the axis is reduced by more than approximately 1 percent, preferablyby more than approximately 5 percent, and particularly preferred by morethan approximately 10 percent relative to the rotational speed at theswitching point in time.

Alternatively, the response point in time can also be defined as thetime at which the axis stops, in particular when its velocity dropsbelow a specified maximum value, preferably approaching zero.

Other criteria can be employed to detect the response point in time, inparticular on the condition that the axis experiences an unacceleratedmotion at the switching point in time, e.g. the velocity of the axis isconstant, that the moment applied by the drive on the axis is constantand the acceleration of the axis is equal to zero.

The response point in time can for instance be a point in time at whicha specified velocity change can be detected. In particular, the responsepoint in time can be defined as the time at which the velocity of theaxis is reduced by more than approximately 1 percent, preferably by morethan approximately 5 percent, and particularly preferred by more thanapproximately 10 percent relative to the rotational speed at theswitching point in time or relative to a maximum velocity of the axis.

The response point in time can for instance also be a point in time atwhich a specified acceleration can be detected. In particular, theresponse point in time can be defined as the time at which theacceleration value of the axis is more than approximately 1 percent,preferably more than approximately 5 percent, and particularly preferredmore than approximately 10 percent relative to a maximum accelerationcapacity or an average acceleration capacity of the drive.

The response point in time can for instance also be a point in time atwhich a specified moment change between the drive and axis can bedetected. In particular, the response point in time can be defined asthe time at which the moment value is more than approximately 1 percent,preferably more than approximately 5 percent, and particularly preferredmore than approximately 10 percent relative to a maximum exertablemoment or an average exertable moment.

Preferably, a combination of two or more of the above criteria can alsobe employed to detect the response point in time.

In another implementation, the response time can in particular be anopening time of the brake. In this case, in one implementation, thebrake is switched in step b) from a closed to an opened state, whereinthe response point in time is then a point in time at which the motionstate of the axis changes, that is to say e.g. the axis begins to move,in particular its velocity exceeding a specified minimum value,preferably differing from zero, or the axis rotating by at least aspecified angle, for instance by at least approximately 1 degree,preferably by at least approximately 5 degrees.

Both implementations can be combined with each other, where in oneimplementation initially the brake in a first step b) switches from anopened to a closed state and determines a response time and/or closingtime, and subsequently, after possibly determining a mechanical play inaccordance with a subsequently explained second aspect of the presentinvention, the brake in a second step b) switches from a closed to anopened state, and an opening time is determined. Conversely, the brakecan initially in a first step b) be switched from a closed to an openedstate, and an opening time can be determined, and the brake subsequentlyin a second step b) can be switched from an opened to a closed state,and a response time and/or closing time can be determined.

In one implementation, a change is detected of the motion state of theaxis and/or the response point in time, in particular a stopping and/ordropping below a specified maximum velocity value and/or a start ofmotion and/or exceeding a specified minimum velocity value, inparticular by means of a position detection device, in particular bydetecting at what point in time a position and/or location, inparticular an angular position and orientation of the axis determined bythe position detection device changes and/or no longer changes.Additionally or alternatively, in one implementation, a change of themotion state of the axis and/or the response point in time is detectedby means of a motion state detection device, for instance a velocitydetection device, an acceleration detection device and/or a momentdetection device, in particular by detecting at what point in time avelocity, in particular rotational speed, of the axis detected by thevelocity detection device exceeds a specified maximum value and/or dropsbelow a specified minimum value, preferably becoming equal to and/orunequal to zero. Additionally or alternatively, in one implementation, achange of the motion state of the axis and/or the response point in timeis detected by means of an acceleration detection device, in particularby detecting at what point in time an acceleration, in particular anangular acceleration, of the axis detected by the acceleration detectiondevice changes and/or no longer changes. For instance, a response pointin time at which the motion state of the axis changes, that is to saye.g. the axis begins to move, can be detected by an accelerationdifferent from zero. The motion state detection device can for instancebe configured as a moment sensor, which is preferably arranged in thearticulated joint between two links of the machine that swivel relativeto each other. Alternatively or additionally, the motion state can bedetected by measuring the current draw of a drive that actuates theaxis.

In one implementation, the switching point in time is a point in time atwhich a switching of the brake is triggered or detected, in particularby means of signaling technology and/or energy technology. Accordingly,in one implementation, the switching point in time is a point in time atwhich a switching of the brake is commanded by signaling technologyand/or a signal to switch the brake is issued or received. In anotherimplementation, the switching point in time is a point in time at whicha switching of the brake is triggered by energy technology and/or anenergy supply for the brake is disconnected or connected and/or such adisconnection and/or connection is detected, in particular by means of asensor.

In accordance with a second aspect of the present invention, a method todetermine a mechanical play of a brake on at least one assigned axis ofa multi-axis machine, in particular a robot or a machine tool, comprisesthe steps:

i) opposing actuation of the axis while the brake is closed; and)

j) detection of a mechanical play between opposing maximum deflectionsof the axis.

In one implementation, this involves detecting the mechanical play whilethe axis is being actuated and/or is in the actuated state in anopposing manner. Preferably, the actuation of the axis can be stoppedwhen the brake response was detected.

In one implementation, the steps i), j) are repeated one or severaltimes and/or the axis is actuated several times in an opposing mannerwhile the brake is closed and a (total-)mechanical play is determinedfrom individual mechanical plays detected during this process betweenthe opposing maximum deflections of the axis. The (total-)mechanicalplay can in particular be a maximum, minimum, or average of theindividual mechanical plays. In this manner, the precision and/oraccuracy of the determined mechanical plays can be advantageouslyimproved.

As already discussed above, the first and second aspects are or can becombined with each other in one implementation, in particular byinitially closing the brake while the axis is in an actuated state anddetermining a response time and/or a closing time, and subsequentlyactuating the axis one or several times in an opposing manner while thebrake is (continues to be) in a closed state and determining amechanical play, and subsequently opening the closed brake with the axisin an actuated state and determining an opening time. In the samemanner, only the first or only the second aspect can also be implementedin one implementation. Accordingly, the aforementioned and subsequentexplanations relate to the first as well as the second aspect.

In one implementation, the axis is actuated by a motor, in particular inan opposing manner and/or in the opposite directions and/or at least ina time period between a switching point in time at which the brake isswitched, and the response time period at which the motion state of theaxis changes.

In one implementation, the axis is actuated with a specified forceand/or the motor applies a specified force on the axis; for purposes ofa more compact description, an anti-parallel force couple and/or torqueis also generalized as a force herein.

A response time and/or a mechanical play can generally be determined ina force-specific manner. As discussed in the beginning, a response timeand/or closing time can be a time between a switching of the brake and aresponse point in time from which point forward the brake causes achange and/or a switch of the motion state of the axis. This can forinstance be effected by the brake applying, and/or having the ability toapply, a certain a minimum brake force, in particular a (maximum)nominal brake force. Analogously, an opening time can be a time betweena switching of the brake and a response point in time, from which pointforward the brake applies, or can apply, no more than only a certainmaximum brake force, and in particular is fully vented and/or at leastessentially applies, and/or can apply, no further brake force.Accordingly, a mechanical play can be the play by which the axis ismoved and/or can be moved by a certain force, in particular in theamount of the (maximum) nominal force.

In one implementation, this force is specified as a function of frictionand/or weight forces, since friction and/or weight forces—that in totalcan counteract the brake and/or support the brake—can be applied on theaxis in addition to the force applied by the motor. As a result, in oneimplementation, a response time and/or a mechanical play can beadvantageously determined in a total force-specific manner, wherein thetotal force and/or the sum of the forces applied on the axis cancomprise the applied friction, weight, and motor forces. In particular,the motor force used to actuate the axis and/or applied to the axis canbe increased by a friction and/or weight force counteracting thisactuation and/or can be reduced by a weight force supporting thisactuation.

In particular when the axis is at rest, the force that needs to begenerated to achieve a position change of the axis depends on thefriction F_(Friction), which is directed approximately equally in bothdirections and gravity F_(Gravity), which is directed directionallydependent. The brake can apply a certain minimum brake force F_(Brake)in both directions. The two maximum forces that need to be applied todetect a play and/or a position difference can therefore be selected inone implementation forF ₁ =F _(Gravity)−(F _(Friction) +F _(Brake)) andF ₂ =F _(Gravity)+(F _(Friction) +F _(Brake)).

The difference of the respectively resulting position of the axis whenforces F₁ and F₂ are applied can define the play.

In particular a weight force, within a certain scope also a frictionforce, depends on the position of the axes of the machine. Accordingly,the force applied by a motor to actuate the axis is specified in oneimplementation depending on the machine position.

The force and/or weight force dependency can be determined in oneimplementation based on a model or on the basis of a precedingactuation.

The motor force used to actuate the axis and/or applied to the axis isspecified in one implementation on the basis of an in particular maximumnominal force of the brake. As already discussed, a response time and/ora mechanical play can be determined in a force-specific manner. Byspecifying the force on the basis of an in particular maximum nominalforce of the brake, a nominal load of the brake can be detectedadvantageously, in particular a response time and/or closing time can bedetermined until the brake applies, or can apply, its nominal force, ora mechanical play at the maximum nominal load of the brake can bedetermined. The force specified in one implementation only represents aportion of an in particular maximum nominal force of a brake, forinstance 10 percent, 50 percent, or 75 percent. This for instance allowsan opening time to be determined in one implementation from which pointforward the brake no longer applies, and/or can apply, this portion,e.g. the axis begins to move.

Additionally or alternatively, the axis in one implementation isactuated by a motor with the specified velocity, in particular arotational speed. In particular, in one implementation, a velocity canbe specified, and the axis can be actuated in a velocity-controlledmanner and/or the motor force actuating the axis can be specified in avelocity-controlled manner, wherein this force can then be limited inone implementation to a specified value, in particular a (maximum)nominal force of the brake. This allows a response time and/or amechanical play to be determined in a particularly easy and accuratemanner.

As discussed in the beginning, having knowledge of a real-time responsetime and/or a real-time mechanical play in particular facilitates amonitoring of a multi-axis machine, in particular a robot, in particularas to whether one or several brakes exhibit excessively large closingand/or opening times and/or mechanical plays, in particular due to wear.Accordingly, in accordance with yet another aspect of the presentinvention, a real-time response time is determined for one or severalbrakes of the machine in accordance with a method described herein, anda fault response is triggered when the determined response time liesoutside of a specified range. Additionally or alternatively, a real-timemechanical play is determined for one or several brakes of the machinein accordance with a method described herein, and a fault response istriggered when the determined mechanical play lies outside a specifiedrange.

In one implementation, the range is specified in each case based on aresponse time and/or a mechanical play determined by previouslyexecuting a method described herein. This allows a change of thebrake(s) to be advantageously detected, in particular recorded.

The fault response can in particular comprise the issuance of a faultmessage and/or a stopping of the machine, in particular a closing of thebrakes(s).

As discussed in the beginning, additionally or alternatively to amonitoring—by taking into account a real-time response time and/or areal-time mechanical play on a multi-axis machine, in particular arobot, the operation of same can be improved. Accordingly, according toyet another aspect of the present invention, a real-time response timefor one or several brakes of the machine is determined according to amethod described herein, and the machine is operated by taking thisresponse time into account, in particularly by planning its motion, inparticular by specifying, in particular by adjusting, the points in timeof opening and/or closing commands in a control program for the machineon the basis of the determined response time(s). Additionally oralternatively, a real-time mechanical play on one or several brakes ofthe machine is determined in accordance with a method described herein,and the machine is operated by taking this response time into account,in particular by planning its motion, in particular by specifying, inparticular by adjusting, motion commands in a control program for themachine on the basis of the determined mechanical play.

In accordance with yet another aspect of the present invention, a systemto operate and/or monitor a multi-axis machine, in particular a robot,is arranged based on hardware and/or software technology to execute themethod described herein.

For this purpose, the system is equipped in one implementation withdevices to actuate the axis, devices to switch the brake, and devices todetermine a response time between a switching point in time and aresponse point in time at which the motion state of the axis changes.

In one implementation, the system exhibits position, velocity, oracceleration detection devices to detect a change of the motion state ofthe axis and/or devices to detect the switching point in time at which aswitching of the brake is triggered, in particular by signalingtechnology and/or energy technology means.

In one implementation, the system exhibits devices to actuate the axisin an opposing manner when the brake is closed and devices to detect amechanical play between opposing maximum deflections of the axis.

In one implementation, the system has devices to actuate the axis bymotor with a specified velocity and/or a specified force; in oneimplementation the system has devices to specify the force as a functionof friction and/or weight force, in particular as a function of themachine position, in particular based on a model or based on a precedingactuation, and/or based on an in particular maximum nominal force of thebrake.

In one implementation, the system has devices to operate a multi-axismachine, in particular a robot, in consideration of the response timeand/or the mechanical play, in particular to plan its motion, whereinthe former is and/or are determined and/or detected by the device todetermine a response time and/or the device to detect a mechanical play.

In one implementation, the system has devices to monitor a multi-axismachine, in particular a robot, based on the response time and/or themechanical play, wherein the former is and/or are determined and/ordetected by the device to determine a response time and/or the device todetermine a mechanical play, and devices to trigger a fault responsewhen the determined response time and/or the detected mechanical playlies outside of the specified range.

A means in the sense of the present invention may be embodied by way oftechnical hardware and/or software means, particularly a processing,particularly micro-processing unit (CPU), preferably connected via astorage and/or bus system transmitting data and/or signals, particularlydigital ones, and/or show one or more programs or program modules. TheCPU may be embodied such that commands are implemented to process aprogram saved in a storage system, record input signals from a data busand/or issue output signals to a data bus. A storage system may compriseone or more, particularly different storage media, particularly optical,magnetic, solid matter, and/or other non-volatile media. The program maybe embodied such that it represents and/or can implement the methodsdescribed here such that the CPU can execute the steps of such methodsand thus can in particular operate and/or monitor the machine.

BRIEF DESCRIPTION OF THE DRAWINGS

Additional advantages and features are found in the dependent claims andthe exemplary implementations, wherein, in partially schematic views:

FIG. 1: shows a sequence of a method according to one implementation ofthe present invention; and

FIG. 2: shows a robot with a system to execute the method according toone implementation of the present invention.

DETAILED DESCRIPTION

FIG. 1 shows a sequence for a method according to one implementation ofthe present invention as a function of time t as the abscissa. Theordinate direction shows a solid line with a switching state B of abrake of an axis of a multi-axis robot 2 (see FIG. 2), a dashed linewith a torque curve T of a drive of the axis, a dotted-dashed line witha velocity curve n of the axis, and a dotted line with a partiallydisplayed position curve φ of the axis.

The axis is actuated without braking during a first time period [t₀,t₁]. This involves determining the weight force and friction torques inorder to reduce and/or increase the drive torque T as a function of theposition during the subsequent determination of the response times andmechanical play. For purposes of a more coherent representation, theweight force and friction influences are disregarded in the exemplaryimplementation; in particular, the exemplary implementation can refer tothe first vertical axis of rotation on robot 2 for illustrationpurposes.

During a second time period [t₁, t₅], the axis is actuated based on arotational speed control, wherein a drive torque is limited to a maximumnominal moment T_(max) of the brake.

The brake is switched to a closed state at a point in time t₂. The firstswitching point in time t₂ is detected as the point in time at whichthis switching of the brake is triggered or detected by means ofsignaling and/or energy technology, for instance by issuing or receivinga corresponding closing signal, or by de-energizing an energy supply ofthe actively vented brake. FIG. 1 indicates this as a step in theswitching state B.

At a point in time t₃, the brake begins to apply a braking effect on theaxis. This is initially compensated by a correspondingly increasingdrive torque T of the rotational speed-controlled drive until themaximum nominal torque of the brake is reached. The lag between theswitching of the brake and the start of its braking effect can forinstance be caused by mechanical, hydraulic, pneumatic, (electro-)magnetic, signaling, and/or energy-technology inertia and/orinductivities.

Starting at the point in time t₄, the brake decelerates the axis towardthe drive torque limited to T_(max), until the axis stops at a point intime t₅. This point in time t₅ is detected by a position or velocitysensor of the axis, and is determined as the first response point intime by the control 1 of robot 2 (see FIG. 2).

The control determines a difference between the first switching point intime t₂ and the first response point in time t₅ as the real-timeresponse time and/or closing time t_(close).

During a subsequent third time period [t₅, t₆], the drive actuates theaxis in the opposite direction while the brake continues to be closed,initially with the negative maximum nominal torque T_(max) of the brakeand then again with the (positive) maximum nominal torque T_(max).

In doing so, the position sensor of the axis detects an individualmechanical play s₁ and/or s₂ each between opposing maximum deflections φof the axis (see FIG. 1).

The control 1 uses this information to determine the real-time (total)mechanical play of the brake, for instance by averaging the values s₁,s₂ or by selecting the larger value.

During a subsequent fourth time period [t₆, t₈], the drive actuates theaxis while the brake continues to be closed with e.g. 50% of the maximumnominal torque T_(max) of the brake.

The brake is switched to an open state at a point in time t₇. The secondswitching point in time t₇ is detected as the point in time at whichthis switching of the brake is triggered or detected by means ofsignaling and/or energy technology, for instance by issuing or receivinga corresponding opening signal, or by energizing an energy supply of theactively vented brake. FIG. 1 indicates this as an (inverse) step in theswitching state B.

At the point in time t₈, the braking effect of the brake on the drivetorque has been reduced to 0.5 T_(max), the axis begins to move (n>0).This point in time t₈ is detected by a position or velocity sensor or anaccelerometer of the axis, and is determined as the second responsepoint in time by the control 1.

The control 1 determines a difference between the second switching pointin time t₇ and the second response point in time t₈ as the real-timeopening time t_(open).

The control 1 then plans a motion of robot 2 by taking into accountthese determined real-time response times t_(close), t_(open) byappropriately adjusting the switching points in time for the brake in acontrol program.

The control 1 also monitors the robot 2 and triggers a fault response,for instance by issuing a fault message when one of the determinedreal-time response times or the determined mechanical play lies outsideof the specified range.

The control 1 and the sensors to detect the switching points in time,the change of the motion state and mechanical plays form a system inaccordance with an implementation of the present invention, whichinclude hardware and/or software technology devices arranged to executethe method described herein.

Although exemplary implementations have been explained in the abovedescription, it is hereby noted that a plurality of modifications ispossible. In addition, it is hereby noted that the exemplaryimplementations are merely examples, which are not intended to in anyway restrict the scope of protection, the uses, and the construction.Rather, the preceding description gives a person skilled in the art aguideline for the implementation of at least one exemplaryimplementation, wherein various modifications, in particular withrespect to the function and arrangement of the components described, canbe undertaken without departing from the scope of protection asindicated by the claims and the equivalent combinations of features.

While the present invention has been illustrated by the description ofspecific embodiments thereof, and while the embodiments have beendescribed in considerable detail, it is not intended to restrict or inany way limit the scope of the appended claims to such detail. Thevarious features discussed herein may be used alone or in anycombination. Additional advantages and modifications will readily appearto those skilled in the art. The invention in its broader aspects istherefore not limited to the specific details, representative apparatusand methods and illustrative examples shown and described. Accordingly,departures may be made from such details without departing from thescope or spirit of the general inventive concept.

LIST OF REFERENCE NUMBERS

-   1 Control-   2 Robot-   T Drive torque-   n Rotational speed-   B Brake switching state-   φ Axis position-   t_(( . . . )) (Point) in time

What is claimed is:
 1. A method for determining a mechanical play of abrake of at least one assigned axis of a multi-axis machine, the methodcomprising: opposing actuation of the at least one assigned axis whilethe brake is closed; and detecting a mechanical play between opposingmaximum deflections of the at least one axis.
 2. The method of claim 1,wherein the multi-axis machine is one of a robot or a machine tool. 3.The method of claim 2, wherein the at least one axis is actuated by themotor with at least one of a specified rotational speed, or a specifiedtorque.
 4. The method of claim 1, wherein: opposing actuation comprisesactuating the at least one axis several times while the brake is closed;and detecting the mechanical play comprises determining a totalmechanical play between opposing maximum deflections of the at least oneaxis from individual mechanical plays which are detected during theseveral actuations.
 5. The method of claim 1, wherein the at least oneaxis is actuated by a motor with at least one of a specified velocity ora specified force.
 6. The method of claim 5, wherein the force isspecified as at least one of: a function of friction; a function of agravitational force; or based on a nominal force of the brake.
 7. Themethod of claim 6, wherein the force is model-based or based on aspecified actuation.
 8. The method of claim 6, wherein specifying theforce as a function of a gravitational force comprises specifying theforce as a function of the machine position.
 9. The method of claim 6,wherein the nominal force of the brake is a maximum nominal force.
 10. Amethod of operating a multi-axis machine, the method comprising:determining a mechanical play of a brake associated with at least oneaxis of the machine, wherein: determining the mechanical play comprises:opposing actuation of the at least one assigned axis while the brake isclosed, and detecting the mechanical play between opposing maximumdeflections of the axis; and operating the multi-axis machine takinginto account the determined mechanical play.
 11. A method for monitoringa multi-axis machine, the method comprising: determining a mechanicalplay of a brake associated with at least one axis of the machine,wherein: determining the mechanical play comprises: opposing actuationof the at least one assigned axis while the brake is closed, anddetecting the mechanical play between opposing maximum deflections ofthe axis; and triggering a fault response when the determined mechanicalplay lies outside of a specified range.
 12. A controller for operatingor monitoring a multi-axis machine, wherein the machine includes atleast one assigned axis and an associated brake, the controller havingprogramming code stored on a non-transitory machine readable datamedium, the programming code configured to, when executed by thecontroller, cause the controller to: determine a mechanical play of thebrake of the at least one axis of the machine, wherein: determining themechanical play comprises: opposing actuation of the at least oneassigned axis while the brake is closed, and detecting the mechanicalplay between opposing maximum deflections of the axis; and then take atleast one of the following actions: trigger a fault response when thedetermined mechanical play lies outside of a specified range, or operatethe multi-axis machine taking into account the determined mechanicalplay.
 13. A computer program product for use with a multi-axis machine,wherein the machine includes at least one assigned axis and anassociated brake, the computer program product having programming codestored on a non-transitory machine readable data medium, the programmingcode configured to, when executed by a controller, cause the controllerto: determine a mechanical play of the brake of the at least one axis ofthe machine, wherein: determining the mechanical play comprises:opposing actuation of the at least one assigned axis while the brake isclosed, and detecting the mechanical play between opposing maximumdeflections of the axis; and then take at least one of the followingactions: trigger a fault response when or the determined mechanical playlies outside of a specified range, or operate the multi-axis machinetaking into account the determined mechanical play.